Magnetic system



March 26, 1957 A. J. TYRELL MAGNETIC SYSTEM 2 Sheets-Sheet 2 Filed June 10. .1955

FIG;

I F 0 W INVENTOR United States Patent MAGNETIC SYSTEM Arthur James Tyrell, Bexley, England, assignor, by mesne assignments, to North American Philips Company, Inc, New York, N. Y., a corporation of Delaware Application June 10, 1955, Serial No. 514,663 Claims priority, application Great Britain June 11, 1954 4 Claims. (Cl. 317-201) This invention relates to magnetic systems. The object of the present invention is to provide a magnetic system which is mechanically strong and magnetically substantially stable.

According to the invention, in a magnetic system comprising two magnetically-soft, high-permeability end plates, three or more magnetically-soft, high-permeability pillars, two permanent magnets which are figures of revolution, two magnetically-soft-high-permeability pole-pieces and two non-ferro-magnetic sheaths, all the parts are arranged substantially symmetrically about a line substantially coincident with the axes of the figures of revolution, one magnet is secured with one pole in magnetic contact with one end plate and the other magnet is secured with the opposite pole in magnetic contact with the other end plate, the pole pieces are secured in magnetic contact with v the poles not in magnetic contact with the end plates, the end plates are secured one in magnetic contact with one end of each pillar and the other in magnetic contact with the other end of each pillar and each magnet is wholly enclosed by the associated end plate, sheath and pole piece,

whereby a predetermined magnetic field is provided between the pole pieces and the return flux is carried substantially by the end plates and pillars at or below magnetic saturation thereof. A magnetically soft material is defined herein to mean a material which will carry a fiux :density of 12,000 lines per sq. cm. or more at a value of H of 30 oersteds or less.

The system may comprise substantially triangular end plates and three pillars in magnetic contact with the end plates at positions near the apices of the end plates.

Each permanent magnet may be a cylinder, a hollow cylinder or, as a further alternative may be substantially a section of a cone the largest radius of which is adjacent the associated end plate.

Parts of the end plates which would not contribute sub stantially to the carriage of the return flux may be omitted and those parts of the end plates lying within the largest inner radii of the magnets may be omitted and substituted by non-ferromagnetic parts.

The pillars may be thinner opposite the gap between the pole pieces than at the ends of the pillars.

The invention will now be described with reference to two embodiments thereof, given by way of example, and illustrated in the accompanying diagrammatic drawings, in which:

Figure l is a sectional view of the first embodiment taken along the line II of Figure 2;

Figure 2 is a cross-section taken along the line IIII of Figure 1;

Figure 3 is a sectional view of the second embodiment taken along the line III-III of Figure 4; and

Figure 4 is a cross-section taken along the line IVIV of Figure 3.

Referring now to Figures 1 and 2, a magnetic system comprises two mild-steel end plates 1, three mild-steel pillars 2, two right-cylindrical permanent magnets 3, two mild-steel pole-pieces 4 and two aluminium sheaths 5.

The parts are arranged substantially symmetrically about a line substantially coincident with the axes of revolution of the figures of revolution 3. The upper magnet 3 is secured with its north pole 6 in contact with the upper end plate 1 and the lower magnet is secured with its south pole 7 in contact with the lower end plate 1. The pole pieces 4 are secured one to the south pole surface of the upper magnet 3 and the other to the north pole surface of the lower magnet 3. Each pole piece comprises a raised part 8 at its periphery to compensate for edge elfects in a manner which is known and will not be further described herein. Each pillar 2 is secured at one end to the upper end plate 1 and at the other end to the lower end plate 1. The sheaths 5' are so arranged and so shaped that each magnet 3 is wholly enclosed by the associated end plate 1, sheath 5 and pole piece 4.

The end plates 1 are rounded at the apices and chamfered at the edges 9 in order. to economise in weight by the omission of parts of the end plates which would not contribute substantially to the carriage of the return flux.

The dimension of the parts 1 and 2 are just sufficient to carry the return flux at or about magnetic saturation and the arrangement has a high mechanical rigidity. A substantially constant magnetic field exists in the space 10 between the pole pieces 4.

Preferably the system is manufactured in accordance with ce-pending British Patent specification No. 17,223/ 54 in order that the magnetic field is substantially permanent and not measurably affected. by inadvertant approach of a ferromagnetic object such as the metal part of a tool.

Figures 3 and 4 show a modification of the system shown in Figures 1 and 2 and similar parts are indicated by the same reference numerals in all four figures.

The magnets 3 are substantially sections of hollow cones, the largest radii of which are adjacent the end plates 1, so enabling the height of the system to be reduced. These parts of the end plates lying within the largest inner radii omitted, since they do not assist in carrying the return flux, and are substituted by aluminium plates 11 which are lighter than mild steel. The end plates 1 are chamfered at the edges 13 adjacent the alum plates 11 also to economise in weight. The pillars 2 are thicker towards the ends than towards the centres 12 since a certain amount of leakage flux is carried by the ends.

This embodiment is lighter and more compact than that shown in Figures 1 and 2.

Both in the embodiment shown in Figures 1 and 2 and in the embodiment shown in Figures 2 and 3, the component parts are secured together by bolts (not shown) of brass or bronze.

The magnetic systems according to the invention may provide a field which is substantially constant in the greater part of the space 10; such a field may be desired for use with caroinotron circuit. As an alternative, the field provided may be weak in the centre and be substantially constant over an annular path. As a further alternative, the lines of force may be barrelled at the edges; such a field may be desired for use with some types of magnetron. i

What is claimed is:

l. A magnetic system comprising a pair of coaxial spaced permanent magnets each of which is a figure of revolution, said magnets being axially magnetized with poles of opposite polarity facing each other, a pair of magnetically soft, high-permeability pole-pieces in abutting relationship wi-th opposite end surfaces of said magnets and defining an air-gap therebetween, a pair of magnetically soft high-permeability end plates each in contact with end surfaces of said magnets remote from said polepieces, a non-ferromagnetic sheath surrounding each of said magnets, said magnets, pole-pieces and end-plates being symmetrical about the axis of revolution of said magnets, and at least three magnetically soft high-permeability pillars symmetrically disposed about said magnets and joining said end plates and constituting a closed magnetic circuit with said end plates, magnets, pole pieces and air-gap thereby providing a predetermined magnetic field between said pole-pieces, the return flux of which is substantially carried by said end plates and pillars at a value not greater than the magnetic saturation thereof.

2. The magnetic system of claim 1 wherein the end plates are triangular shaped and three pillars are in mag netic contact with said end plates, said pillars being positioned at the apices of said end plates.

References Cited in the file of this patent FOREIGN PATENTS France Oct. 24, 1938 France Nov. 22, 1945 

